list add
                        new pair(item1, 70)
                        new pair(item2, 50)
                        new pair(item3, 30)
                        new pair(item4, 10)

               int weightSum = sum (each weight from pairs)

               int randomNumber = randomInclusiveRange(0, weightSum);

               for every pair
                       if (randomNumber - weightSum <= 0)
                           choose that item